1. Field of the Invention
The present invention relates generally to chemical mechanical polishing (CMP) systems and techniques for improving the performance and effectiveness of CMP operations. Specifically, the present invention relates to the distribution of micro-abrasive suspension, or slurry, underneath the wafer in CMP operations.
2. Description of the Related Art
In the fabrication of semiconductor devices, there is a need to perform CMP operations, including polishing, buffing and wafer cleaning. Typically, integrated circuit devices are in the form of multi-level structures. At the substrate level, transistor devices are formed. In subsequent levels, interconnect metallization lines are patterned and electrically connected to the transistor devices to define the desired functional device. As is well known, patterned conductive layers are insulated from each other by dielectric materials, such as silicon dioxide, for example. As more metallization levels and associated dielectric layers are formed, the need to planarize the dielectric material increases. Without planarization, fabrication of additional metallization layers becomes substantially more difficult due to the higher variations in the surface topography. In other applications, metal line patterns are formed in the dielectric material, and then metal CMP operations are performed to remove excess metallization, e.g., such as copper.
In the prior art, CMP systems typically implement belt, orbital, or brush stations in which belts, pads, or brushes are used to scrub, buff, and polish a wafer. Slurry is used to facilitate and enhance the CMP operation. Slurry is most usually introduced onto a moving preparation surface, e.g., belt, pad, brush, and the like, and distributed over the preparation surface as well as the surface of the semiconductor wafer being buffed, polished, or otherwise prepared by the CMP process. The distribution is generally accomplished by a combination of the movement of the preparation surface, the movement of the semiconductor wafer and the friction created between the semiconductor wafer and the preparation surface.
FIG. 1A illustrates an exemplary prior art CMP system 100. The CMP system 100 in FIG. 1A is a belt-type system, so designated because the preparation surface is an endless belt 108 mounted on two drums 114 which drive the belt 108 in a rotational motion as indicated by belt rotation directional arrows 116. As used herein, the belt 108 should be understood to include a polishing pad or other preparation surface material in addition to any supporting material, such as aluminum, stainless steel or any suitable supporting structural material for holding the pad or other preparation surface. A wafer 102 is mounted on a carrier 104. The carrier 104 is rotated in direction 106. The rotating wafer 102 is then applied against the rotating belt 108 with a force F to accomplish a CMP process. Some CMP processes require significant force F to be applied. A platen 112 is provided to stabilize the belt 108 and to provide a solid surface onto which to apply the wafer 102.
Slurry 118 is introduced upstream of the wafer 102. In a belt-type CMP system 100, slurry 118 is commonly introduced in a region that is upstream and off-center from the wafer 102 as illustrated in FIG. 1A. The movement of the belt 108 carries the slurry 118 to the wafer 102 which is mounted on the carrier 104 and being applied against the belt 108 with a force F as it is being rotated 106. The rotation 106 of the wafer 102 and the friction of the wafer 102 against the belt 108 further distributes the slurry 118 across and into the polishing pad or other preparation surface of the belt 108 and over the surface of the wafer 102. In FIG. 1C, the effect of the moving belt 108 and the rotating wafer 102 is illustrated. As the slurry 118 approaches the wafer 102 from upstream and off-center, it is distributed across the belt 108, facilitating the CMP operation and moving beyond the wafer 102 having been distributed across a larger region of the belt 108. Slurry 118a is shown after passing the wafer 102 and having been distributed across the belt 108 during the CMP operation on wafer 102.
Slurry 118, as is known, is a water-based suspension consisting of dispersed micro-abrasives, dissolved chemicals and in some cases, lubricants. The fluid properties of the suspension allow for the even distribution of the abrasive material across a surface and enhance the effectiveness of the CMP operation. Both solid abrasives and fluid chemicals, including water, modify the surface properties of interacting objects, thus promoting smooth removal. A section of a typical CMP belt 108 and the porous texture of the polishing pad or other preparation surface is illustrated in FIG. 1B. As stated above, the belt provides the supporting structure for the polishing pad or other preparation surface. In FIG. 1B, the polishing pad surface of the belt 108 is shown as uneven or rough and contributing an abrasiveness. Slurry 118 is distributed over the pad surface 108, but due to the fluid properties, the micro-abrasives, surface tension, capillary openings in the belt 108 surface blocked by air, and other such factors, the slurry does not penetrate into the surface cavities through the usual distribution method described above. FIG. 1B shows capillary openings blocked by air pockets 119 that form in the surface cavities and result in uneven and unstable slurry distribution. Non-uniform slurry distribution can result in less efficient and non-uniform planarization of wafers being processed. Further, if slurry 118 loses the fluid properties due to build-up and drying, then the micro-abrasives collect and xe2x80x9ccakexe2x80x9d forming chunks of abrasive debris. This abrasive debris, in the extreme, can damage the quality of the semiconductor wafer being processed in a CMP operation. Typically, such debris contributes to non-uniform planarization and wafer defects. In addition to the air pockets 119 shown in FIG. 1B, the polishing pad surface 108 can accumulate build-up of dried slurry 118. As the slurry build-up dries, chunks of abrasive debris form.
One method of removing and preventing build-up on the pad surface 108 is illustrated in FIG. 1A. A belt conditioner assembly 110 is mounted down-stream from the wafer 102. The belt conditioner assembly 110 consists of an abrasive head that is applied against the polishing pad surface 108 to dislodge any abrasive debris that may be on the polishing pad 108. Further, the belt conditioner assembly 110 renews the surface cavities in the polishing pad 108 to ensure the pad 108 retains its abrasive properties, and the ability to hold and transport slurry into the CMP operation. As the belt continues to rotate, the conditioner assembly 110 provides constant conditioning of the pad 108 during CMP operations. Or, the conditioning assembly 110 can be programmed to condition the pad 108 at intervals according to operator requirements.
The increased complexity of multi-layered semiconductor chips requires more precise and more uniform planarization techniques. CMP is and will remain an integral part of the semiconductor wafer manufacturing process, but must be made more effective and more controllable to meet the increasing demands for more complex fabrication. In view of the foregoing, there is a need for slurry distribution methods and apparatus in CMP operations that are more controllable, that more evenly and uniformly distribute slurry across a preparation surface, and that minimize the risks of damage due to dried slurry and abrasive debris.
Broadly speaking, the present invention fills these needs by providing systems and methods for the uniform and even distribution of slurry in a CMP system. The gimbaled roller system and method provide a controllable distribution of slurry to create a more efficient and effective CMP operation with fewer substrate defects. It should be appreciated that the present invention can be implemented in numerous ways, including as a process, an apparatus, a system, a device or a method. Several inventive embodiments of the present invention are described below.
In one embodiment, an apparatus for even slurry distribution in CMP operations is disclosed. The apparatus is a gimbaled roller consisting of a roller, a gimbaling roller attachment attached to the roller, and a positioning arm attached to the gimbaling roller attachment to position the roller for the even distribution of slurry.
In another embodiment, an apparatus for distributing slurry over a polishing pad surface used in chemical mechanical polishing of a substrate is disclosed. The apparatus includes a belt assembly having the polishing pad surface that rotates in a loop. A roller is positioned over the polishing pad surface and has a gimbaling attachment configured to ensure that a surface of the roller is maintained substantially parallel to the polishing pad surface.
In still a further embodiment, a method for distributing slurry in a chemical mechanical polishing system is disclosed. The method includes introducing slurry onto a chemical mechanical polishing surface and moving the chemical mechanical polishing surface. The method further provides applying a roller against the chemical mechanical polishing surface as the slurry is moved on the moving chemical mechanical polishing surface toward the roller, and distributing the slurry as an even film over the chemical mechanical polishing surface.
In yet another embodiment, an apparatus for combined pad conditioning and slurry distribution is disclosed. The apparatus includes a polishing pad with a polishing pad surface, and a first and a second roller positioned before a wafer polishing application location. The first roller has an abrasive surface that is applied to the polishing pad surface, and the second roller is defined below the polishing pad surface to support the polishing pad at a location where the first roller is applied. Thus configured, the first roller conditions the polishing pad surface and distributes slurry over the polishing pad surface.
The advantages of the present invention include the providing of more control over the chemical mechanical polishing operation. The present invention allows for the setting and maintaining of a designated thickness of slurry on a polishing pad or other preparation surface. By applying pressure with a gimbaled roller of the invention, air pockets are displaced in the porous surface of the polishing pad, and slurry is distributed in an even and uniform thickness across the pad. The slurry is also distributed across the width of the polishing pad surface of the belt resulting in a uniform and controllable amount of slurry at the substrate for CMP processing. More control over the slurry in CMP operations yields more precise processing with fewer defects.
Other aspects and advantages of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the present invention.